Effect of ECAE-processing on the thermo-mechanical behavior of Ti34 wt.%Nb0.14 wt.%O shape memory alloy

Abstract

The effect of ECAE (equal channel angular extrusion)-processing on the thermo-mechanical behavior of Ti34 wt.%Nb0.14 wt.%O shape memory alloy was studied by measuring the tensile stress-strain curve at various temperatures and using DSC. X-ray diffraction, and TEM. An ultrafine (0.4 mu m) grain structure was developed by severe plastic deformation and by the formation of alpha-particles on grain boundaries, which was facilitated by oxygen. Severe grain refinement led to a large decrease of M-s from 216 degrees C to 106 degrees C. Furthermore, the elimination of oxygen by alpha-particles led to an abrupt decrease of the stress for reorienting the martensite variants and to an increase in the transformation strain. Subsequent omega-aging treatment further stabilized the beta-phase at room temperature, resulting in a superelastic property. (C) 2012 Elsevier B.V. All rights reserved.